The Dungeon Journal has been updated to note that a Mythic-only Scalecommander Sarkareth mount customization will drop — the Embodiment of the Hellforged Dragonriding customization!
In previous expansions, some final Mythic final bosses would drop a unique mount. However, in Dragonflight with Dragonriding mounts, Blizzard has opted to go for amazing Dragonriding customizations instead. In Vault of the Incarnates, the Dragonriding Customization was Renewed Proto-Drake:
